In their simplest form, sondes consist of a detecting or sensing element e.g., an electrode, a probe, etc. and electronic circuitry for processing signals supplied by the element. Metering apparatuses also generally comprise a display means or some other means for transmitting the results to users.
Since their introduction into the industry, metering apparatuses have gone through various advancements. An example of one such advancement is the implementation of micro-processors which enable the use of several electrodes or probes within one unit. An example of a multi-probe metering apparatus is disclosed in U.S. Pat. No. 4,608,532, incorporated herein by reference.
Since its introduction into the industry, the multi-probed metering apparatus has been extensively used. In a specific form of conventional multi-probed metering apparatuses, the plurality of electrodes/probes are generally combined into a single mechanical housing referred to hereinafter as a "sonde". This design facilitates transport of the apparatus. Moreover, the implementation of a sonde for the housing of a plurality of electrodes/probes reduces the number of cables and components necessary in such multi-probed devices.
In their simplest form, multi-probed metering apparatuses have the ability to measure a plurality of parameters, one such parameter being associated with each individual electrode/probe. The sonde units of conventional multi-probed devices generally comprise some sort of means for selecting which electrode's/probe's signal will be monitored at a given point in time.
After a particular electrode/probe has been selected, the analog signal produced thereby is processed. This signal can be processed in many different ways. Examples of such ways include: (a) sending the analog signal from the selected electrode/probe directly to an instrument or user for measurement, analysis, calibration, display and/or storage; and/or (b) sending the analog signal from the selected electrode/probe to a central processing unit, wherein the analog signal is first digitalized, and then transmitted to an instrument or user for measurement, analysis, calibration, display and/or storage.
Although they are extensively employed in the industry, many of the conventional multi-probed metering apparatuses have inherent limitations and/or problems associated therewith. These limitations and/or problems are due, in part, to their specific design and/or their limited circuitry.
One major problem associated with many conventional multi-probed metering apparatuses pertains to their inability to consistently reproduce measured parameters accurately, when the signal from the electrode/probe has to be transmitted over a substantial distance. Specifically, sonde units of some multi-probed metering apparatuses first measure a specific parameter and convert this measurement into an analog signal. This signal is then sent to a central processing unit where it is digitalized and/or processed.
When the distance between the sonde unit and the central processing unit is substantial (i.e., generally anything over ten meters), the signal generally begins to deteriorate. This deterioration skews the accuracy of the measurement being monitored.
One method of attempting to overcome this problem is by employing highly-sophisticated analog cabling between the sonde unit and the central processing unit. While this technique can work under certain conditions, it is very expensive. Specifically, high quality analog cabling retails for approximately $3 to $10 per meter. If the sonde unit is employed, for example, to measure various parameters in water at depths of over 100 meters, it can easily be seen how the cost of employing the aforementioned technique to overcome this particular problem can become very expensive.
Another method of attempting to overcome the problem associated with accurately reproducing measured parameters and transmitting these measurements over a substantial distance is by programming the central processing unit to compensate for the deterioration of the transmitted signal. This method can successfully be employed, but only under those circumstances where all other variables (e.g., distance between electrodes and central processing unit, ambient temperature, solution temperature, etc.) remain relatively constant. However, since in the analytical world nothing remains constant, and since multi-probed metering apparatuses are generally used under a multitude of differing conditions, this technique of overcoming the problem is generally unfeasible.
Accordingly, a multi-probed metering apparatus which can accurately reproduce the measurements from its sonde unit, without substantially increasing the cost of the device, would be a welcome improvement in the industry. It would be an even more welcomed improvement if this high level of reproducibility could be accomplished when the sonde unit is a substantial distance from the central processing unit.
Another problem associated with many of the conventional multi-probed metering apparatuses pertains to the scope of their functions (i.e., the flexibility of the metering apparatus). Specifically, many of the conventional multi-probed metering apparatuses have virtually no flexibility since they are merely able to display the monitored information.
Some conventional multi-probed metering apparatuses, however, have associated therewith a limited amount of flexibility due to their capability of being interfaced with other devices. Examples of devices which can be interfaced with some of the conventional multi-probed metering apparatuses include: (a) control means which can trigger various functions such as the sounding of an alarm, the opening/closing of a valve, etc., and/or (b) computers for compiling and/or processing the monitored information.
Due to their limited amount of flexibility, most conventional multi-probed devices are limited, in the field, to their specific internal software design, if any. Therefore, if one desires to change some of the parameters, to analyze a measured parameter, or to calculate a non-measured parameter from measured parameters, traditionally, the metering apparatus has to be interfaced with some sort of external memory storage and/or data processing source (e.g., a computer).
Since it is often desirable to change parameters, analyze measured parameters, and/or calculate non-measured parameters on site, and since it is cumbersome to continually have a computer available, it would be a welcomed improvement in the industry if a multi-probed metering apparatus can be designed to make elaborate mathematical computations without having to be interfaced with an external memory storage and/or data processing source.
When monitoring specific parameters of a fluid with a multi-probed metering apparatus, it is often desirable to have the fluid continually flowing over the electrodes. Therefore, when the fluid is stagnant, an external fluid flow-maintaining means is conventionally employed.
Many of the conventional multi-probed metering apparatuses which employ such a fluid flow-maintaining means do so by the implementation of an external stirrer unit. In conventional apparatuses, this external stirrer unit is an independent component generally attached to the opposing face of the sonde unit such that the propeller of the stirrer unit is pointing back towards the plurality of electrodes/probes. This conventional external stirrer unit is generally connected to the central processing unit by a separate external cable.
While the conventional external stirrer design does maintain the flow of fluid over the electrodes/probes, there are inherent problems associated therewith. One such problem pertains to size. Generally, due to the presence of the external stirrer unit and the separate external cable therefor, the sonde unit becomes bulky and difficult to handle.
Another problem associated with employing an external stirrer component pertains to the separate, external cable between it and the central processing unit. As stated earlier, the sonde unit can be located at distances of over 100 meters from the central processing unit. In the first instance, there is an inherent cost associated with connecting the stirrer to the central processing unit which the user would obviously like to avoid. Furthermore, since the separate cable between the external stirrer unit and the central processing unit is external, it is susceptible to the conditions in which the electrodes have been submerged. These conditions often have an adverse effect on cable, and especially at its connection points. Accordingly, the external cables associated with conventional stirrer units have to be frequently repaired, maintained and/or replaced.
In view of the above, it would also be a welcomed improvement in the industry if a method could be devised to minimize the cost of employing, maintaining and/or replacing the means for maintaining a fluid flow over the electrodes/probes.
Yet another problem associated with the conventional external stirrer units pertains to their amount of energy consumption. Specifically, stirrer units inherently consume a large amount of energy. Since most multi-probed metering apparatuses are commonly used in the field, they are generally run from battery packs. Since the life of a battery depends largely upon the energy being consumed, it is desirable to minimize the amount of energy consumed for extraneous purposes (e.g., running a stirrer). However, as indicated earlier, it is also desirable to have the fluid flowing over the electrodes/probes, as opposed to being stagnant. In view of the above, the industry is faced with a dilemma. Accordingly, it would be another welcomed improvement if a means could be devised to maintain fluid flow over the electrodes/probes, while minimizing the amount of energy consumed.
Yet another problem associated with many of the conventional multi-probed metering apparatuses pertains to their methods of calibration. For example, most multi-probed metering apparatuses are calibrated by the following technique. First, a calibration solution, useful for calibrating one specific parameter (e.g., "zeroing") of one specific electrode/probe, is placed into a calibration bath. Since all electrodes/probes of most conventional metering apparatuses are housed in one sonde unit, all electrodes/probes are dipped into this specific calibration solution. The one electrode/probe relating to the specific calibration solution in the bath is then calibrated.
Thereafter, that particular calibration solution is discarded from the bath; and the electrodes and the solution container are rinsed. This filling-calibration-rinsing process is then repeated for each of the remaining electrodes until all are calibrated for that specific parameter (e.g., zeroed). However, since in many instances electrodes/probes also have to be calibrated for other parameters (e.g., "slopes"), this generally means that the aforementioned filling-calibration-rinsing process has to be repeated for each electrode/probe with a second type of calibration solution.
As can be seen, the conventional method of calibrating multi-probed meters is extremely time-consuming. Moreover, although the electrodes/probes, which have been subjected to the aforementioned conventional calibration technique, are rinsed after each calibration, they are, at least to some degree, contaminated by the other various calibration solutions (e.g., pH electrodes can be contaminated by turbidity calibration solutions). Accordingly, a device or technique which simplifies the calibration of multi-probed metering apparatuses and/or eliminates the contamination of the various electrodes/probes by extraneous, non-related, calibration solutions, will be yet another welcomed improvement in the industry.
Even another problem associated with many of the conventional multi-probed metering apparatuses pertains partially to repairing and/or replacing damaged electrodes/probes, and partially, to changing the parameters which the electrodes/probes monitor. Specifically, since many of the conventional multi-probed metering apparatuses are used to measure various parameters in fluids (e.g., water), the connections between the electrodes/probes and circuitry within the sonde unit must remain dry. Therefore, the sonde unit must be water-tight. Due to this requirement, many sonde units are factory sealed. Therefore, if a particular electrode/probe has to be repaired or replaced for one reason or another, the entire sonde unit generally has to be taken out of commission and returned to a shop where the work can be performed.
If the metering apparatus is being employed to continually monitor specific parameters, this generally requires a user to have more than one sonde unit available on site. Since the sonde units can retail from between $1,000 up to $5,000, depending upon the number of electrodes/probes and the circuitry therein, it is very costly to have a number of sonde units available on site. Accordingly, another welcomed improvement in the industry would be a multi-probed metering apparatus designed for field replacement and/or repair of electrodes/probes without destroying the necessary water-tight configuration of the sonde unit.